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BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1a and 1b are a side view and a top view of a
conventional acoustic lens, FIG. 2 is a perspective view with a part of the acoustic lens of this
invention removed, and FIG. It is sectional drawing of the state which attached the acoustic lens
to the baffle plate. Reference numeral 212 denotes a recess, 211 denotes a flat plate, 213
denotes a base, and 21 denotes an acoustic lens.
DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement
of a speaker system, particularly, a tf echo lens for noise reduction in a small speaker system
such as a car. In general, it is known that sound waves emitted from a speaker exhibit a sharp
directivity along the axial direction of the speaker at Q equal to or higher than a frequency
proportional to the effective vibration area of the speaker. For Kono, especially in the so-called
tweeter, which is a speaker that reproduces high-pitched tones, this tendency is remarkable 1 O
1 i =) 15 '7' An attempt has been made to place the acoustic lens in front of the opening of the
sunker in order to reduce the complexity of the directivity and to obtain a uniform sound
pressure over a wide range. There is. For example, one form of the acoustic lens 101 shown in
FIG. 1 (2) and (2) forms a concave portion 11 in the central part of each [Likely the front end of
the flat plate 12 is inclined downward, that is, Parallel fixed, which is coupled to the opening of
the speaker 2. According to the above configuration, as is well known, a sound path is formed
between the speaker 2 and the atmosphere by the parallel flat plate 12, and furthermore, the
length of the sound path in the horizontal direction is different due to the concave portion. As a
result, the convex phase wavefront as schematically shown by the broken line shown in FIG. 2 is
formed, and the directionality is relaxed. On the other hand, as a drawback of the acoustic lens,
the flat plate 12 is excited by a sound wave passing between parallel flats 1i 12 & 'i effect causes
self-resonance and 10 ν 7)) sound generated thereby is reproduced sound from the speaker 2
And cause distortion in reproduction. In particular, conventionally, an 'aluminum plate with small
internal loss has been used as the material of the parallel flat plate 12, and the small acoustic
lens causes the self-resonance due to the small mechanical strength due to the shape of the flat
plate 12. There is a big tendency. Therefore, in this invention, at least the parallel flat plate 12
portion (hereinafter referred to as a blade) of the acoustic lens having the above configuration is
formed of a mixture of polypropylene and calcium carbonate to remarkably suppress the selfresonance. explain in detail. "7 +" Th Fig. 2 is an acoustic lens 210 of this invention-羽-! A
plurality of blades 211 formed of a mixture of polypropylene and calcium carbonate (50 wt% of
polypropylene and 50 wt% of calcium carbonate, t% in the example) is a perspective view from
which a portion is removed It is formed so that its front end is inclined downward, that is, parallel
to the base 213 so as to be inclined with respect to a horizontal plane and mounted at equal
In addition, the base 211 is provided with an attachment hole 214 for fixing to the porous plate
81, and further, an opening 215 is bored in the center of the base 213, and a rear surface of the
opening is perforated. B, in the middle land configuration, at least the blades 211 vc) are formed
of the above mixture, and the base 218 can be bonded and the fusion father can be bonded using
other means, but by integral molding etc. 11 and a base 213-one sq, 8.7-five, five o'clock 63, a
three. (In the case of a very high production cost). Fig. 3 n sectional plate 31 acoustic crosssectional view showing the coupling structure of the 7's 21's beaker 2. The speaker 2 is fixed to
the opening 215 of the speaker 2 from the rear surface of the base 213 to the opening 215 by
screws or the like. Do. Then, the base 213 is inserted into an opening portion formed in the baffle
plate 31 and fixed with a screw or the like. As described above by way of example in the above
embodiment, 1) 079)) 1 °° ′ ′ ′ ′ ′ ′ 8 ′ ′ * I # vyi ′; t ′ ′ O ′ b: a <==. It is
made of a mixture of polypropylene and calcium carbonate in the blade field which is the main
generation part of the self-resonance, and polypropylene has a significantly larger internal loss
(tan δ) compared with other synthetic resins, so that the resonance of the blade part Is
suppressed, the occurrence of abnormal noise is significantly reduced, and it is possible to make
a good reproduction metal with less distortion. Also, carbonic carcicum increases the density to 1
• at the same time as compensating for the stiffness of the wing and the resonance by the weight
increase. It also has the effect of lowering the frequency, and it is also possible to select the
content in a timely manner in accordance with various design requirements such as the shape
and dimensions of the blade. Further, according to the mounting structure shown in this
embodiment, since the speaker and the acoustic lens can be connected in advance, by performing
preliminary processing outside the process in the production process, the baffle plate is formed
by one mounting process in the manufacturing process. It is possible to mount an acoustic lens
and a speaker on one side, thereby reducing the number of man-hours and preventing the
occurrence of mounting errors. In general, in this type of on-vehicle system, a speaker is attached
to the back of the baffle plate and an acoustic lens is attached to the front of the baffle plate
independently, or more, and the thickness of the baffle plate between the both. While the air gap
portion corresponding to the above is formed, and the original function of the acoustic lens is not
sufficiently obtained, it is possible to couple the acoustic lens and the speaker in close proximity
in the above-mentioned mounting structure. It has excellent effects on performance and
manufacturing, such as being able to prevent defects.